These 99. cent lights (scroll down the page) are also nice giveaways and cheap enough to put one in every bag just in case. I just listed them as an alternative to the slide switch type aloha mentioned. I have both types and so far I like the squeeze lights better. Not to mention, in my experience the plastic swivel piece on the slide switch lights tends to break rather easily. But really, they're both a good deal.

http://www.lighthound.com/index.asp?PageAction=VIEWCATS&Category=133